# Help System

This chapter describes the Help system in the GNOME Desktop.

## Introduction to the Help System

The GNOME Desktop displays help in the Yelp Help browser. For more information, see Yelp Help Browser in the GNOME Desktop User Guide.

The source documents for the help are XML files. The XML files are written to the DocBook XML Version 4.1.2 document type definition (DTD). The DocBook XML files are converted to HTML using stylesheets installed with gnome-doc-utils and the HTML is displayed in the help browser. For more information on DocBook XML, see the following URL:

          http://www.oasis-open.org/docbook/xml

The Help system uses Open Source Metadata Framework (OMF) files, and a cataloging system. The next sections describe OMF files and the cataloging system.

## OMF Files

The XML file for each manual has an associated OMF file. The OMF file contains information about the manual that is used by the Help browser. OMF files have a `.omf` extension.

When you install an application, the installation process installs an OMF file to a directory of OMF files. If a Help document has an associated OMF file in an OMF file directory, the Help document is displayed in the Help browser.

OMF files contain information about Help documents such as the following:

- The location of the XML file for the Help document

- The title of the Help document

- A subject category to which the Help document belongs

For more information on how to create OMF files, please see Writing Scrollkeeper OMF Files.

## ScrollKeeper Cataloging System

ScrollKeeper is a cataloging system for documentation. Its primary function is to manage the information in OMF files for the help browser. When you install an application, the OMF file is copied to the ``$prefix`/share/omf/`<application-name>`` directory.

ScrollKeeper builds a table of contents from the collection of OMF files in the directories specified in ``$prefix`/etc/scrollkeeper.conf` file. This file usually consists of a single line with the `OMF_DIR` set to a comma separated list of directories to recursively search.

    OMF_DIR=/usr/share/omf:/usr/local/share/omf:/opt/gnome2/share/omf:/opt/kde/omf

ScrollKeeper contains a hierarchy of subject categories to which a help document can belong. The subject category of the document in the OMF file determines the location of the document in the table of contents presented by the help browser.

The hierarchy of subject categories is defined in the file ``$prefix`/scrollkeeper/Templates/`<lang>`/scrollkeeper_cl.xml`. The subject category of a document must correspond to a category specified in this file.

For more information on the Scrollkeeper system, visit the website at http://scrollkeeper.sourceforge.net/.

If the help document XML file is moved to a new location, then the location in the OMF file needs to be updated.